For the actuation of magnetic valves, a current, ideally a constant current is required, that is flowing through its valve coil, which is known as accurately as possible.
If a current regulation for actuating a magnetic valve is to be used, it may be put into effect using a relatively costly circuit configuration, which therefore does not represent a cost-effective design approach.
Other known methods and devices, used for the above purpose, are based on resistance measurement via resistance dividers or resistance bridge circuits, or measurement methods using alternating voltages and/or alternating currents.
Instead of a current regulation, current control may also be used by which the current flowing through the valve is controlled as a function of various environmental parameters, and which may have a good regulating quality of the current similar to that which is known of current regulation. For this purpose, multidimensional characteristics maps may be used in connection with a microcontroller control.
The supply voltage UB and the temperature of the valve coil, for instance, are also taken into account in the current as the parameter for the current control. The recording of the supply voltage may take place via a resistance divider, for example, in this instance. However, in this case the measurement of the temperature of the coil is costly, since the latter influences the internal resistance Rcu of the coil, according to the equation Rcu=R20×(1+α×ΔT). Since the coils in question usually have a low internal resistance of a few Ohm, measuring the temperature of the coils via resistance dividers or resistance bridges cannot be carried out, as a rule.
In addition, a device for monitoring and compensating changes in a coil resistor of injector nozzles, of an internal combustion engine during use, is discussed in document US 2005/071098, in which a very small preset current is conducted through the coil of a magnetic valve during its use and when the magnetic valve is in a switched-off state established by pulse width modulation. While the current flows through the coil, the voltage at the coil is measured and the resistance of the coil is calculated from Ohm's law. If the actual resistance is known, the pulse control factor of the pulse width modulation for the compensation of a resistance deviation is changed.
Furthermore, document KR 2004 0068769 A discusses a temperature measuring device of a magnetic valve coil in which a temperature change of the magnetic valve coil is recorded, and a current corresponding to the recorded temperature change is supplied.
Finally, document U.S. Pat. No. 4,636,620 A discusses a control system having temperature compensation for an injector nozzle of an internal combustion engine, which uses the value of voltage levels at the nozzle coil to determine the temperature of the coil.